docs(readme): keep quickstart runnable

The quickstart now uses uv-managed module execution so the README works from a fresh checkout without requiring manual virtualenv activation. This keeps the documented path aligned with the project's src layout and setup flow.

Constraint: Quickstart steps should work without requiring manual venv activation
Rejected: Add a separate venv activation step | more shell-specific and easier to skip
Confidence: high
Scope-risk: narrow
Reversibility: clean
Directive: Keep README command examples aligned with the uv-managed workflow unless setup semantics change
Tested: uv run python -m python_template --help; uv run python -m python_template hello; python -m python_template --help (fails as expected without uv run)
Not-tested: Full CI suite (docs-only change)

Author: yujeongdev

README.md

@@ -19,8 +19,8 @@ cheap enough to run all the time.
 ```bash
 make setup-dev
 make check
-python -m python_template --help
-python -m python_template hello
+uv run python -m python_template --help
+uv run python -m python_template hello
 ```
 
 Sample output: